Switching mechanism



Aug. 13, 1940. D. G. TAYLOR 2,211,735

SWITCHING MECHANISM Filed May 7, 1957 4 Sheets-Sheet l 9/ L go yimmmnmwllg Aug. 13, 1940. D. G. TAYLOR 2,211,735

swITGHING MEGHANISM Filed May 7, '1957 4 sheets-sheet 2 Aug. 13, 1940.

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D. G. TAYLOR swITCHING MECHANISM Filed May '7, 1937 4 Sheets-Sheet 4 Patented Aug. 13, 1940 UNITED STATES PATENT OFFICE SWITCHING LIECHANISM Application May 7, 1937, Serial No. 141,297

28 Claims.

This invention relates to switching mechanism and more particularly to a type of mechanism adapted to open and/or close a circuit upon change in the value of a. condition.

5: Any resilient body such for example as a bellows, or a coil spring, if unopposed by any external force, has a natural or normal length or shape. Take the bellows for example; if unopposed by external forces any particular bellows will assume l a certain normal length. Now if a slight compressive force is applied to the bellows it will be compressed slightly until the resilience of the bellows itself develops an equal force to balance the original applied force. An increase in the applied l force will compress the bellows further until its resilience develops an equal and opposite force to balance it. The rate at which the bellows develops the internal balancing force for the external applied force is called the spring rate of the bellows.

Assume now that a bellows is fixed at one end and free at the other and that the free end is operating between two stops. Assume also for example that a pressure of iive pounds within the bellows is required to start to move its free end.

Due to its spring rate the pressure must graduallylincrease, say to ten pounds, to gradually move the bellows from one stop to the other. In other words, each time the bellows is moved slightly it develops an additional internal force to balance the external force which caused its movement, so that for every external pressure of from five to ten pounds the bellows has a corresponding length. This is the normal operation of a bellows.

Suppose, however, that it is desired to have the bellows operate so that a force which is great Ienough to start to move the bellows is suflicient to continue its movement throughout its entire n stroke. To do this, it is necessary to develop a force which is exactly equal and opposite to the force developed in the bellows due to its spring rate; or in other words, it is necessary to compensate the spring rate of the bellows. 'I'his force must equal zero when the bellows is in one position and must increase gradually and oppositely to the resilient force in the bellows as it moves from one position to another. 'I'he external force moving thelbellows will now be unopposed and will therefore move the bellows the entire distance of its stroke without stopping.

The same principle may be applied in compensating the springrate of the coil spring.

It is therefore an object of this invention in a control device having a main adjusting spring (c1. zoo-fsa) which is alternately compressed and elongated durlng'the normal operation of the device to provide mechanism for compensating the spring rate of such adjusting spring.

It is also an object of this invention, where a l resilient condition responsive device is used, such as a bellows, for example, to provide mechanism for compensating the spring rate of such condition responsive device.

A further object is to compensate the spring rates of all resilient members which affect the operation of a control member so that the control member will operate over its entire range of movement after it has once been started by the condition responsive device which controls it.

An additional object is the provision of an improved contact structure operable to maintain a contact in association with another contact vwith a relatively great pressure until such time as the mechanism moving the contact has moved to such 20 a point that the contacts will be relatively rapidlyl separated.

A further object is the provision of such a mechanism wherein the contact pressure of a pair of opposed contacts. will remain'relatively great until such time as the contacts are opened abruptly or with a snap action.

A still further object is the provision of an improved means of compensating for the increased force exerted by a spring opposing a condition responsiye element in combination with a contact structure in such manner that the compensating spring will serve to separate said contacts relatively rapidly but only after a relatively substantial movement of the condition responsive element.

An additional object is the provision of an improved leverage arrangement whereby arelatively slight movement of a condition responsive element is amplified to a relatively great movement of a contact, such leverage arrangement serving simultaneously to eliminate what is known in the art as vanishing contact pressure. In devices of an analogous nature hitherto constructed considerable diculty has existed in that as a condition responsive element moved slightly in response to a change in the value of a condition, the pressure of a contact moved thereby against an adjacent contact was lessened a corresponding amount. Accordingly, at one point in the movement of the 5o operating mechanism, the contacts were in engagement but the force exerted to hold said contacts in engagement was so slight that vibration resulted which frequently occasioned arcing between the contacts. 'I'his defect is known as vanishing contact pressure. It is, therefore, an object of this invention to preclude vanishing contact pressure since with the structure to be hereinafter described a relatively firm engagement of the contacts is maintained until such time as the operating mechanism has moved sufficiently to separate the contacts a relatively great distance relatively rapidly.

A further and more specific object of this invention is the provision of improved means properly to regulate the force exerted by either or both of the resilient means utilized to obtain the result just described.

A further object of this invention is the provision of an improved artificial knife edge con-- struction obviating the necessity of preforming certain parts of the mechanism with a. relatively fine knife edge, the artificial knife edge structure accomplishing all the advantages of such a structure preformed as above mentioned.

An additional specific object of the invention is the provision of an improved scale plate adapted to be utilized in connection with the mechanism to be hereinafter described whereby an instrument may be calibrated without adjustment of interior mechanism.

A further specific object is the provision o1 improved means for adjusting the tension or compression of a spring adapted to act against the force exerted by a condition responsive element to move a contact or analogous mechanism.

A still further specic object is the provision of mechanism embodying the features above and to be hereinafter described which is relatively simple and inexpensive in construction and is sturdy, durable and reliable in operation.

Other objects will in part be obvious and in part pointed out hereinafter.

The invention accordingly consists in the combinations of elements, arrangements of partsand features of construction, all as will be more fully described hereinafter and shown in the accompanying drawings.

Referring now to the drawings wherein are shown several illustrative embodiments of the invention:

Figure 1 is a perspective view of one form of .switching mechanism embodying features of the line 6-6 of Figure 5 as viewed from the bottom;

Figure 7 is a side elevational view of the mechanism shown in Figures 5 and 6, parts thereof being shown in a different position;

Figure 8 is a perspective view showing certain other features of the structure shown in Figures 5, 6 and 7;

Figure 9 is a sectional view along the line 9-9 of Figure 6 as viewed from the left;

Figure 10 is a side sectional view taken along the line Ill-I of Figure 7 as viewed from the left;

Figure 11 is an enlarged elevational view, partly schematic, showing certain details of construction;

Figure 12 is a side elevational view partly in section of a still further form of switching mechanism embodying certain features of the instant invention;

v Figure 13 is a fragmentary view showing certain portions of the structure shown in Figure 12 in a different position;

Figure 14 is a fragmentary perspective view showing certain portions of the mechanism shown in Figure 12;

Figure 15 is a sectional view taken along the line ||5 of Figure 13 as viewed from the top;

Figure 16 is a front elevational view of a still further modified form of the invention certain parts being removed for the sake of clarity;

Figure 17 is a view similar to Figure 16 but showing the parts in a dierent position, certain parts thereof being cut away in order that certain other parts may be more clearly shown;

Figure 18 is a side sectional view taken substantially along the line |B-I8 of Figure 16 as viewed from the left, certain parts thereof being cut away and certain other parts being omitted;

Figure 19 is al detailed side sectional view taken along the line |9-I9 of Figure 16 as seen from the left, certain parts thereof being broken away;

Figure 2O is a reduced perspective view showing a portion of the exterior of the casing utilized with the instrument shown in Figures 16, 17 and 18 showing certain features of the invention;

Figure 21 is an enlarged sectional view taken along line 2|-2I of Figure 17, and

Figure 22 is sectional view taken along the line 22-22 of Figure 21, certain parts thereof being broken away.

Similar reference characters refer to similar parts throughout the several views of the drawings.

Referring now to the switching mechanism disclosed in Figures 1 to 4, inclusive, 30 indicates a mounting or base plate to which is secured a casing or housing 3| in any suitable manner, as by threaded engagement of a threaded extending portion 32 with a suitable threaded aperture in base plate 30. A projection 33 extends from housing 3| to which may be secured any suitable pressure or other condition responsive mechanism. Such mechanism is not shown but may readily take the form of a conventional bulb and capillary tube arrangement. Housing 3| contains a bellows 34 of conventional construction biased upwardly as by a spring 35, a guide member 36 being provided to prevent complete collapse of bellows 34, in the absence of any pressure thereon. Bellows 34 is secured to the base plate 31 of casing 3| in any suitable manner as by soldering as shown at 38. An operating rod 39 is secured to the upper portion of bellows 34 in any suitable manner as generally indicated at 40. Operating rod 39 extends upwardly through an aperture 4| in extending portion 32 of casing 3| and likewise, therefore, through the threaded aperture in plate 30. Thus, it will be seen that changes in pressure or temperature or other condition affecting the previously mentioned bulb is transmitted in a known manner through the capillary tube to cause expansion or contraction of bellows 34 and hence vertical movement of operating rod 39.

Secured to base plate 30 is a second plate 42, the securing means takingany desired form such as screws 43. Plate 42 has an upwardly extending portion 44 and an inwardly extending portion 45 on which is fulcrumed, in a manner to be hereinafter described more fully, a lever 46. Lever 46 is secured, as better shown in Figure 3, to operating rod 39 by means of a pin 41 passed through suitable apertures in lever 46 and operating rod. 39. Thus, movement of operating member 39 is transmitted to rotative movement of the distal end of lever 46 about the pivotal mounting on portion 45. A second lever or link 48 is also pivotally secured to the distal end of lever 46. A stop member comprising a depending lug 49 is formed on the end of lever 46 and adapted to abut lever 48 :for a purposelto be described hereinafter. The other end of lever 48 is pivotally associated with a pair of-projections 50 carried by,a member 5| which is in turn pivotally mounted in upstanding lugs 52 carried by plate 42. Member 5| carries a block of insulating material 53 to which is secured a resilient bar 54 carrying contacts 55 and 56. Member 5| has at its upper extremity a projection 51 havingan aperture therein to which is securedl one endof a spring 53. The other end1of spring 58 is secured to a bar 59 having an aperture 68 -therein through which operating rod 39 passes. Aperture 60 is of elongated shape to permit movement of bar 59 with respect tto operating rod 39. Base plate 38 has secured thereto in any desired manner a post which serves as a support for bar 59. A screw 66 passed through a second aperture 61 also of elongated shape engages a suitably threaded aperture in the upper end of post 65. A downwardly depending portion 61a of bar 59 is provided with a suitably threaded aperture through which is passed a screw 68 adapted to abut post 65.

Thus from .the foregoing, it will be seen that rotation of screw 68 causes movement of bar 59 and a corresponding variation in the tension of spring 58, elongated apertures 60 and 61 permitting limited motion of bar 59. It will also be seen that screw 66 serves as a clamping or locking means to hold bar 59 in any position to which it may be moved by rotation of screw 68.

Operating rod 39 extends upwardly through an aperture 69 in lever 46 and thence through a suitable aperture in a supporting member 18 se- .cured to plate 42, as by screws 1|, then passing sired manner, as by embedding the end thereof in a suitably formed aperture in the `upper end of operating rod 39. 'I'he other end of spring 16 is engaged by bushing 12 and hence .bar 14.

y Thus, it will be seen that rotation of screws 15 varies the position of bar 14 with respect to supporting member 10 'and` operating rod 39 and consequently the tension of spring 16.

VBase plate 38 has an upwardly extending por- Y tion to which are secured insulating blocks,` 8|

as by screws 82, the other end of screws 82 engaging an insulating member .83 as shown at 84. In-

tacts 85 and 86 are so positioned as to engage contacts 55 and 56, respectively, when .the device operates in the `manner to be hereinafter described.

Hereinbefore the pivotal mounting of several of the parts with rel/ation to\other parts has been mentioned. This pivotal mounting may be of any desired type but may also advantageously take the for-naci the mounting disclosed in Figure 4. This construction provides all the advantages of knife edge pivotal mounting and obivates to a large extent the necessity for fine machining of certain of the parts. Thus as shown in Figure 4, the pivot pin may take the form of a block 99 which may be substantially rectangular in cross section and have a relatively flat surface 9| in place of the conventional knife edge. An aperture 92 is provided to receive pivot pin 90. In configuration aperture 92 is comprised of apair of relatively fiat sides 93 and 94 disposed in acute angular relationship to each other and forming stops to limit the pivotal movement of member by abutment with the opposed flat sides 95 and 96 thereof. The side 91 of aperture 92 adjacent the angle formed [by sides 93 and 94 is convexly arcuate in configuration with respect to side 9| of pivot pin 90. Thus it will be seen, that side 9| is in tangential relationship to the -arc of side 91 at all times regardless of its position of adjustment with respect to angularly disposed sides 93 and 94 and that thus iby this point-to-point contact a structure providing the full equivalent of a knife edge is provided at a relatively small cost and with `a minimum of machining of the parts.

The operation of the structure hereinbefore discussed is as follows. Assuming the parts to be in the position shown in Figure 1, an increase pressure causes bellows 34 to expand and move operating rod 39 upwardly. Movement of operating rod 39 causes movement of pin 41 and consequent movement ci lever 'i6 about the fulcrum provided by extending 'fiortion 45. Such upward movement, in turn, causes pivotal movement of lever 48 and consequently permits spring `,58 to cause inward movement of projections 59 and member 5| which is, in turn, pivoted to lugs 52y and consequent separation of contacts 54 and 55 with contacts 85 and 86, respectively, the mechanism then assuming the position shown in Figure 2.-

It will also be seen that as operating rod 39 moves upwardly, the tension of spring 16 is increased requiring a relatively greater force to complete the movement of operating rod 39 to its uppermost limit and the consequent complete separation of contacts 55 and 56 from contacts 85 and 86. It is also true that an increasing force is necessary to continue to expand bellows 34 and that the force exerted by the spring 35 decreases as the bellows 34 expands. The force necessary to balance the variations in these forces is supplied by spring 58 in the following manner.

t will be seen that with the parts in the position shown in Figure 1, the fulcrums of levers 46 and 48 and the projections 50 of member 5| lie in straight line relationship and that spring 58 exerts a force on member 5| in a direction in substantial parallelism to the above mentioned -straight line relationship. Thus, the component of force exerted by spring 58 is ineffective to occasion any pivotal movement of levers 46 and 48 o r member 5|. Correspondingly, the contacts 55 and 56 .are held in engagement with their opposed contacts 85 and 86 through the pressure through the levers 46 and 48. The greater the exv exerted not only by the abutment of levers 46 and 48 with extension 50 of member 5| but also by the normal resiliency of resilient bar 54, it being noted that the arrangement of the parts is such that when levers 46 and 48 are in the above mentioned straight line relationship, the contacts 55 and 56 are forced into relatively close association with opposed contacts and 86 in such manner that energy is stored up in bar 54 to insure a relatively firm contact pressure. However, immediately upon disruption of this straight line relationship, spring 58 begins to exert a force to rotate member 5| about its pivot positioned in lug 52. As the disalignment increases, the component of force exerted by spring 58 is increased and by suitable adjustment of screws 68 and 15 such increasing force may be arranged to exactly compensate for the variations in forces due to the spring rates of the main adjusting spring 16, the bellows 34, and the biasing spring 35. When springs 58 and 16 are so adjusted, it will be seen that the movements of contacts 55 and 56 towards or away from their opposed contacts 85 and 86 vwill be relatively slow but steady and continuous upon the achievement of a predetermined condition in bellows 34. Thus, for example, if the bellows 34 is sc arranged as to operate to open the contacts upon the achievement of live pounds of pressure, the contact will be fully opened upon the achievement of such ve pounds of pressure. Assume, for example, that the parts are in the position shown in Figure 1. At this time the spring 58 can exert no force tending to move the operating rod 39 vertically because the force exerted by the f spring 58 is transmitted through the levers 48 and 46 whose fulcrums are located in the same straight linel so that no turning force is transmitted to the lever 46 and therefore the force has no vertical component affecting the operating rod 39. As the bellows 34 starts to expand, the operating rod 39 will rotate lever 46 slightly about its fulcrum 45 which will disalign the fulcrums for the levers 46 and 48. This means that the force exerted by the spring 58 will now have a small vertical component due to the angle between the levers 46 and 48. As the bellows expands, its own internal force resisting expansion will increase and the force of the tension spring 16 resisting expansion of the bellows will increase and the force exerted by the spring 35 aiding this added expansion of the bellows will decrease. As a result, if the original yforce is to be suicient to move the bellows throughout its entire stroke an additional force must be addedaiding expansion of the bellows which is equal to the sum of the changes inthe three forces just mentioned. This additional force is supplied by the spring 58 pansion of the bellows 34, the greater will be the additional force required and the greater the vertical component of the force exerted by the spring 58 due to the fact that the angle between the levers 46 and 48 will have increased. The size and strength of the spring 58 is so selected that as the bellows expands the vertical component of the force exerted by this spring will exactly compensate the variations in the forces due to the bellows and the two springs 16 and 35. Therefore, after the bellows 34 once starts to expand it will continue to expand until it has moved through its entire stroke because the spring rates of the bellows and the two springs 16 and 35 will have been compensated and the expanding force acting on the bellows will be unopposed. It will also be readily understood that by further suitable adjustment of screw 68, spring 58 may be tensioned to such a .point that as the straight line relationship of levers 46 arid'"48 is disrupted the component of force exerted by spring 58 is greater than the increased force due to the spring rates of the various elements whereby the contacts will engage or disengage with a relatively abrupt or snap action.

While in the above the mechanism has been discussedas operating upon opening movement, it will readily be seen that the same results are achieved upon closing movement. As the bellows 34 contracts from the position shown in Figure 2, the resiliency in the bellows tending to cause such contraction will decrease and the force exerted by spring 16 tending to cause contraction of the bellows will decrease and the force exerted by spring 35 opposing such contraction will increase. Therefore, if it is desired that the force permitting the bellows to start its downward stroke shall be suiicient to move it throughout its entire stroke, it will be necessary to compensate for the variations in the above forces. This is accomplished by the eect of spring 58 on the operating rod 39 through the levers 46 and 49. In the vposition shown in Figure 2, this spring will be exerting its greatest force which is tending to hold the rod 39 in its upper position.v However, after the rod once starts moving down under the influence of bellows 34, that component of force exerted by the spring 58 will decrease due to the fact that the angle between the levers 46 and 48 is decreasing and this component of force decreases in accordance with the variations in the above mentioned forces until the bellows has reached the position shown in Figure 1, at which time the spring 58 will exert no force tending `to move the operating rod 39 vertically. Thus it will be seen that the spring rates of the bellows 34, spring 16, and spring 35 have been exactly compensated for so that once a force is developed suiciently to start the bellows from either end of its stroke that force will be suiiicient to move it throughout its entire stroke So thatthe parts will never be in an intermediate position.

Refering now to the form of mechanism shown in Figures 5 to 11, inclusive, |66 generally indicates'a mounting plate to which is secured in any suitable manner a housing |6I. Contained i within housing IUI is a bellows |62 suitably secured to a plate |63 which is, in turn, secured peripherally to housing |6I in a fluid tight manner. A suitable volatile fluid or other condition responsive media may be contained in housing |6| and serve through variations in the condition to which it is responsive to expand or contract the bellows |62, such contraction or expansion serving to move a plate |64 secured to the lower end of the'bellows. Secured in any suitable manner to plate"|64 is an operating member |65 which extends upwardly outv of housing I6|. For convenience in replenishing the volatile uid or other media contained in the housing |6|, a passageway |66 is provided in operating member |65 and closed by a screw |61 having a point serving to form a needle valve as shown at |68.

A spring |69 surrounds operating rod |65 and a conventional shield AI I6 is provided to prevent complete collapse of bellows \|62. 'Ihe lower end of spring |69 abuts the plate `|64 and the upper end is in abutting relationship with a collar III having a centrally positioned aperture ||2 through which operating rod |65 projects. Col-` 75 lar ||I is provided with a pair of oppositely disposed depressions Illa for a purpose to be more fully described hereinafter. A member II3 ifs" threaded into a suitable aperture in operating rod |05 and carries at its extremity a pivot pin I4 upon which is mounted a lever I5. Lever ||5 is comprised of a channel shaped member and carries adjacent an extremity a pair of downwardly depending lugs I I6 through suitable apertures in which a pin ||1 is passed carrying a pair of roller contacts II8. The opposite end` of lever ||5 has a' pair of oppositely disposed apertures |I9 adapted to engage the opposite ends of a pivot pin or bar |20 whereby the lever ||5 is Iulcrumed on pin |20. Bar |20, in turn, comprises a portion of a member I2| which is secured as by screws |22 to a supporting frame |23 whchis secured in any suitable manner as by screws |24 to baseplate |00. Supporting` member' |23 is comprised of a top portion |25 'having an elongated aperture |26 therein and a plurality of Pairs of downwardly extending legs |21 having outwardly turned portions |28 through apertures in which screws |24 are passed to engage suitable threaded apertures in'base plate |00. An upwardly turned lug |30 is formed integral with or may be attached to upper surface |25 of supporting frame |23 and has a threaded aperture passed therethrough. A screw I3| of substantial length passes through aperture in lug |30 and engages a threaded aperture |40 in a lug |32 carried by a movable member |33. Member |33 is comprised of an extending portion |34 having apertures 35 adjacent the extremities thereof .and a downwardly depending portion |36 which extends into slot |26 and is, in turn, provided with outwardly flared lugs |31 to hold member |33 in related assembly with slot |25 (see Figure 10).

Thus it will be seen that rotation of screw. |3I varies the position of member |34 with respect to the lengthofslot |26. Lever ||5 is provided with a pin |42 projecting therethrough at a point adjacent the roller contacts IIB. Pin |42 provides securing means for the ends of a pair of coil springs vE43, the opposite ends of which engage apertures I35. Thus, it will be seen thaty varying the position oi screw |3I and hence lug |32 and member |33 varies the tension in springs |43 in a manner and for a purpose to be hereinafter described. l

Roller contacts ||8 are positioned for engagement with either of two pairs of stationary contacts |50 and |5|, and |52 and |53, respectively. Contacts |50 and |5I, |52 and |53 are carried by suitable resilient supporting arms secured, as by screws |54, to an insulating block |55 carried in turn by a bracket |56 secured, as by screws |51, to base plate |00. An insulating member |58 is also secured in a similar manner to bracket |51 and serves as a stop member to 'f preclude downward movement of roller contacts ||8 beyond a position of engagement with contacts |50 and |5I. Suitable lead wires (not shown) maybe secured by screws |54I to establish electrical contact with contacts |50, 5|

|52 and |53.

A lever |60 is mounted on a suitable pivot |6I carried by one pair of legs |21 of supporting frame |23. Lever |60 is provided with a bifurcation comprised of two extending members |64, each-'being provided with a downwardly extending pointed projection |65 adapted to engage depressions Ia of collar I. The opposite end of lever |60 is provided with an angularly disposed portion |61 having a pair or downwardly depending lugs |68 through which are passed apertures to maintain therein the extremities of a pin |89 supporting a roller |10.

Positioned on base plate is a cam |1| provided with a plurality of ridges on its upper surface, the ridges being so spaced that the depressions therebetween are of suiiicient extent to engage roller |10. Cam |1| is mounted on a rotatable member |12 provided with a centrally disposed axle |13 which extends through an aperture in base plate |00. A knob |14 is positioned on the outer extremity oi axle |13.' Thus it will be seen, that rotation of knob |14, in turn, rotates axle |13, member |12 and hence cam I1I. Cor- 'respondingly, it will be seen that as cam |1| is rotated, roller |10 engages the various depressions hereinbefore described between the ridges on the cam surface of cam |1I and that each of .these ridges is positioned at a different height on the cam surface so that that end of lever |60 carrying roller |10 is raised or lowered in accordance with the position of cam I1I-, such raising or lowering varying the position of collar |II through the engagement of projections |65 with depressions Ia to vary the compression of spring |09. y

It may here be pointed out that lever I I carries an insulating shield |80 secured thereto as by rivets I8| and that such insulating shield is provided with an extending portion |82 between roller contacts |I0 and pin |42 in order to pre` clude the establishment of an arc therebetween.

In operation of the device, as the volatile iiuid in casing IOI expands, bellows |02 is contracted to force operating rod |05 upwardly and hence member ||3 and its associated pivot I4 whereby lever I|5 is moved to displace contacts ||8 from engagement with contacts |50 and |5I as shown in the position of Figure 6, and force them into engagement with the contacts |52 and |53, as shown in Figure 7. Springs |43, it will be noted, exert an upward component of force upon lever I5 only when the straight line alignment of contacts II8, pin |42,n pin IH and the pvot |20 are displaced. When the parts, ior example, are in the position shown in Figure 6, the component of force exerted by springs |43 is ineffective to move lever I|5 and hence roller contacts I|8. However, upon a slight increase in pressure, the straight line relationship of the parts is disturbed and the tension of springs |43 is immediately effective, acting through pin |42 to move lever ||5 upwardly about its iulcrum |20 to the position shown in Figure 7. Correspondingly, relief of pressure in housing |0I causes expansion of bellows |02 whereupon the spring |09, which it should be pointed out is considerably more powerful than both oi' springs |43, moves bellows |02 and consequently roller contacts I I8, through operating member I 05, downwardly into engagement with contacts |50 and |5|.

It will be seen, therefore, that the springs |43 serve to compensate for the increasing component of force exerted by the increased compression of spring |09 as operating member |05 is moved upwardly and also for the additional force required to further expand bellows |02, for as the compression of spring |09 is increased the tension of springs I 43 acting in a direction opposed to the component of force exerted by spring |09 is correspondingly increased and upon the achievement of a given pressure upon bellows |02, the roller contacts |I8 may be moved from their position position of engagement with contacts |52 and |53. It will also be seen that the speed of movement of the contacts may be readily Varied by a simple adjustment of the tension in springs |43 through movement of screw |3| and that the compression of spring |09 may be readily varied byrotation of knob |14 and consequent rotation of cam I1|.

- Accordingly, the speed of movement of roller contacts ||8 from one position to the other may be readily varied as may the pressure required to be exerted upon bellows |02 to move contacts ||8 fromone position of engagement to the other.

Referring now to that modication of the invention disclosed in Figures 12 to 15, inclusive, a base plate 200 has secured thereto a housing 20|. Such securing may take the form of passing a threaded portion 202 of housing 20| through a suitable aperture in plate 200 and securing a nut 203 thereon. Housing 20| has a base plate 204 to which is secured a bellows 205 suitably sealed against pressure. To a downwardly extending portion 206 of base plate 204 threaded as shown at 201 may be attached any suitable pressure or temperature or other condition responsive device (not shown) but which may conveniently take the form of a conventional pressure tube leading to a source of pressure. A spring 208 normally -biases bellows 205 upwardly as viewed in Figure 12. A guide member 209 is also provided to prevent collapse of bellows 205. Secured to the upper portion of bellows 205 is a lug 2 I0 adapted for engagement with the threaded end 2|| of an operating rod 2|2. Operating rod 2|2 is provided with a pair of oppositely disposed notches 2|3 and 2|4 at one point of its length. The purpose and function of these notches will be described hereinafter.

Secured to base plate 200 is a supporting frame 2| 5, such securing means taking the form of rivets 2|6. Supporting frame 2|5 has two inwardly turned lugs 2|1 adapted to support a disc 2|8 rigidly secured to operating rod 2I2. Disc 2|8 is formed with a ridge 2| 9 thereon and supports a coil spring 220. The upper end of spring 220 abuts a member 22| provided with an extending lug 222 which projects into a slot 223 in frame 2|5. Projecting through suitable apertures in the top of frame 2|5 and member 22| is a screw generally indicated at 224 having a head 226 and threaded as at 225. Thus it will be seen that rotation of head 226 of screw 224 moves member 22| upwardlyor downwardly, this member being precluded from rotation by the projecting lug 222, to increase or decrease the compression of spring 220 for a purpose to be described hereinafter. Likewise, it will be seen that expansion of bellows 205 moves operating rod 2|2 upward` ly-against the compression of spring 220, such compression as above stated being adapted to be varied by rotation of screw 224.

Carried by a pair of lugs 230 struck from supporting frame 2|5 is a block 23| pivoted as by a pivot pin 232 to lugs 230. Block 23| is provided with a notch 233 corresponding in configuration and disposed adjacent to notch 2|4. A toggle member 234 provided with a double knife edge is tted between notches 2|4 and 233. It will thus be seen that movement of operating rod 2|2 imparted to toggle 234 results in a pivotal movement of block 23|. an extending projection 235 formedwith a hook 236 adapted to engage an end 231 of a coil spring 238. 'Ihe other end of coil spring 238 is secured to a threaded member 239 carrying a projection 240 adapted to engage in a slotted aperture 24| Block 23| is provided with= in supporting frame 2|5. A screw 242 is passed through an aperture in a projection 243 struck outwardly from frame 2|5 and engages the threaded interior portion of threaded member 239. Thus, it will be seen that rotation of screw 242 results in varying the tension imparted to spring 238 since the projection 240V is rigidly affixed to threaded member 239 and rotation of screw I242 can consequently result only in an increase or decrease in thevtension in spring 238.

A lever 250 having a pair of knife edged surfaces 25| and 252 is positioned adjacent notch 2|3 in such a. manner that knife edge 25| engages,

As better shown in Figure 15, lever 250 is bowed outwardly to extend around framework 2|5 and has a link 251 secured to its outer end as by a pivot pin 258. Link 251 may be comprised, if desired, of two link like members (see Figures 14 and l5). A pivot pin 259 secures a pair of links 260 and 26| to the end of link 251 opposite pin 258. Link 26| is pivoted as by a pin 262 to a projecting member 263 secured in any desired manner as byrivets 264 to the outer surface of supporting frame 2|5. Link 260 is pivotally secured as by a pin 265 toa mid-portion of an arm 210 which, in turn, is pivoted as by a pivot pin 21| to the extremity of projection 263. The lower end of arm 210 carries an insulating block 215 which, in turn, carries a resilient arm 216 having a cross piece 211 carrying contacts 218. An insulating block 219 is secured as by screws 280 to a portion of base plate 200. Insulating block 219 carries a pair of contact clips 28| each of which carries a contact282 positioned for engagement with contacts 218. Contact clips 28| are in electrical association with terminal clips 283 to which suitable conductors (not shown) may be attached.

Thus, from the foregoing it will be seen that as the pressure in the bellows 205 is increased, operating rod 2 l 2 is moved upwardly against the pressure of spring 220. Such upward movement results in a corresponding upward movement of the inner knife edges of lever 250 and toggle 234 to cause the parts to assume the position shown in Figure 13. It will be noted that the contacts 218 and 282 engage before the lever 210 attains its nal position.v The completion of the movement of lever 210 is permitted by the exing of the resilient arm 216. This upward movement of knife edge 25| causes a downward movement of lever 250 causing link 251 to be moved downwardly and links 260 and 26| to assume the straight line position shown in Figure 13 forcing arm 21|) outwardly and hence contacts 218 into engagement with contacts 282. Upon a relief of the pressure in bellows 205, spring 220 forces operating rod 2 I2 downwardly and causes link 234 and lever 250 to reassume the position shown in Figure 12 whereupon by upward movement of lever 250 contacts 218 are caused to separate from con.

tacts 282. As has been pointed out'in connection with other forms of structure embodying the invention, as the pressure in bellows 205 forces operating rod 2|2 upwardly, the compression of spring 220 occasions a greater resistance and the bellows 205 requires a greater force to complete, in this case, the closing of the contacts. In order that no more pressure need be supplied in bellows 205, spring 238 is provided. Since it will be readily seen that as the compression of springl220 is increased, so likewise,I is the tension of spring 238 slightly increased and that as levers 250 and toggle 234 assume the straight line relationship shown in Figure 13, block 231 is correspondingly pivoted in a direction away from operating rod 212 and correspondingly extension 235 is moved downwardly slightly to increase the tension on spring 238.

The device may be so adjusted that upon the achievement of a given pressure in the bellows, the contacts will be closed Without any subsequent increase in pressure being required. As soon as the compression of spring 220 is increased, the component of force exerted' by spring 238, which it will be noted is directed in the same direction as that exerted by spring 220, is decreased to compensate for such increased compression. It will also be understood that by suitably varying the tension of spring 238, a varying operating differential may be readily achieved. Correspondingly, if the tension in spring 238 is considerably greater than the compression in spring 220, the contacts will close relatively rapidly and with a comparatively snap action. If, however, the springs are so adjusted that the force component of spring 238 merely equalizes the increasing force component of spring 220, the contacts, will move comparatively slowly and smoothly into and out of engagement. It will also be seen that by the unique leverage arrangement above described, a substantial multiplication of motion is provided imparting a relatively slight movement of the bellows to the contacts as a relatively great movement thereof.

It willy be noted that the mechanical advantage of the operating rod 212 over the movable contact arm 210 is iniinitely great at the position where the levers 260 and 261 are in a straight line relation, and this mechanical advantage is reduced rapidly as the levers leave the straight line relationship so as to give an increased movement of the movable contact arm. This high mechanical advantage near the straight line position o1' levers 260 and 26| makes possible arelatively large force for holding contacts 218 and 282 together and pulling them apart and when the levers leave the straight line position the movable contact moves more rapidly to`suf1iciently separate the two contacts.

It might also be pointed out that when the levers 260 and 261 are in a straight line position they can transmit no force tending to move operating rod 212. This means that any variation in the contact pressure between contacts 218 and 282 cannot be transmitted to rod 2 I2 to affect the pressure at which the bellows opens the contacts.

It will also be seen that when the parts are in the position shown in Figure 13, the component of force exerted by spring 238 upon contacts 218 is substantially zero since the straight line relationship of extension 235, link 234, lever 250 and contacts 218 permit substantially no mechanical advantage of the spring over any of these parts. However, as soon as this straight line relationship is disrupted, the tension of spring V238 becomes correspondingly felt and functions in the manner above described.

n Thus it will now appear that the combination of the above described spring arrangement, leverage arrangement and straight line relationship results in a structure which will achieve the objects of the invention in an advantageous and reliable manner.

Having reference now to the structure shown in Figures 16 to 22, inclusive, which comprises a switching mechanism embodying certain features of this invention as shown in the preceding modiiications as well ascertain additional features, a casing 300 is disclosed to which. is secured in any suitable manner, as by screws 301, a housing 302. Positioned within housing 302 is a bellows 303 of conventional construction having a bottom plate 304 to which is secured an operating rod 305 provided with a tip 308 and a nut 301 forming an annulus. A sleeve 308 comprising an integral part of housing 302 extends downwardly to a position spaced from base plate 304 and has an inwardly turned flange 309 forming a seat for an end of a coil spring 310, the other end of which abuts annulus 301. A suitable plug 311 may comprise a substantially integral part of housing 302 and has threadedly engaged therewith a capillary tube 312. Capillary tube 312 may extend to a suitable uld filled condition responsive bulb of any desired construction (not shown). Thus, a change in the value of a condition adjacent the bulb will by volatilization of the fluid contained therein cause expansion and contraction of bellows 303 and consequently upward and downward movement of operating rod 305 in a well known manner.

The pointed tip 306 of operating rod 305 engages a recess 315 in a cup-like member 316 rigidly secured to a lever 311. Lever 311 is pivotally mounted on a pair of knife edges 318 which comprise portions of an extending member 320 secured in any desired manner to casing 300, it being pointed out that notches 319 are provided in lever 311 to accommodate knife edges 318. A portion of member 320 extends through a suitable aperture in a lug 321 which extends upwardly from the base of casing 300 to provide a relatively rigid mounting for knife edges 318 (see Figure 16). The opposite end of lever 311 is movable between the head 325 of a screw 326 and the end 321 of a second screw 328, the screws being secured by nuts 329 and 330 respectively to the lower Wall of casing 300 and extending therethrough. Thus it will be seen that by suitable rotation of screws 328 and 328, the range of movement of lever 311 may be varied. Rigi dly secured to lever 311 in any desired manner is an upwardly extending portion 331 provided at its end with an inwardly extending portion 332 provided with a recess 333 and with a projection 334 intermediate its length. Pivotally secured to projection 334 as by a pivot 335 is a link 336. Link 336 is pivoted at its' other end as by a pivot 331 to a downwardly extending lug 338 carried by an arm 340. Arm 340 has a second downwardly depending lug 341 which is pivotally mounted as by a pivot pin 342 in a bracket 343 which, in turn, is

rigidly secured as by screws 344 to a side wall of casing 300. The distal end of lever 340 has secured thereto as by rivets 350 a block of insulating material 351. Positioned adjacent the extremity of block 351 is a contact structure carrying contacts adapted to engage other contacts, all as will be more fully pointed out hereinafter.

Thus from the foregoing, it Will be seen that upon an increase in pressure or temperature, bellows 302 is contracted to move operating rod 305 upwardly and hence move lever 311 about its fulcrum on knife edge 318 until it assumes the position shown in Figure 17, correspondingly, moving member 331 into the position shown in Figure 17 whereupon link 336 will move about its pivots 335 and 331, respectively. in turn acting against lug 338 to rotate arm 340 about its pvot 342 and move insulating block 351 and its associated contact structure upwardly into engagement with the opposed contacts. Upon a decrease in pressure means now to be described are provided to reopen the contacts.

Lever 3 I 1 is provided with a notch 355 having a recess 356, as better shown in Figure 19, therein. Positioned adjacent this notch is a plug 351 having a knife edge 358. Plug 351 is provided with an upwardly extending portion 368 and is of such Y configuration with respect to recess 356 that normally it will not pass therethroughand so positioned that knife edge 358 engages notches 355. One end 36| of a spring 362 engages a suitable recess in upwardly extending portion 368. The other end of spring 362 is secured to a member 363 having an internal threaded aperture therein through which is passed a screw 364 which, in turn, passes through a suitable aperture inthe upper wall of casing 388. Screw 364 is provided with a head 365 having a groove 366 therein for suitable engagement by a tool for al purpose to be later described. Comprising an integral part of of different values may be required to move the contact structure to closed position in the manner previously described. Upon relief of such pressure, it will be understood that spring 362 moves lever 3|1 to return the contacts to open position. It will be understood, however, that as the contacts move from open to closed position and lever 3H moves downwardly, the tension in spring 362 is increased and accordingly to fully open the contact an increasing force must be exerted by operating rod 385. In order that the contacts may open fully upon the achievement of a predetermined pressure or other condition, suitable means now to be described are provided to compensate for such increased tension in spring 362 and also for the increased force required to move bellows 383.

Secured to the back wall of casing 388 is a mounting bracket 315 having an inwardly extending portion 316 and a portion 311 positioned in parallel relation to the back wall of casing 388. Portion 311 is provided with a slotted aperture 318 through which is passed a pivot pin 319 held in position by a lock nut 388. Upon release of lock nut 388, it will be understood that the position of pivot pin 319 in slotted aperture 318 may be varied for a purpose to be later described. Mounted on pivot pin 319 is a lever 38|. Lever 38| is provided with a downwardly extending portion 382 and an angularly disposed portion 383. Portion 383 is provided with an aperture through which is passed one end 384 of a spring 385. The other end of spring 385 carries a member 386 of configuration similar to member 363 and having an internally threaded aperture therethrough. A screw 381 is passed through the aperture in member 386 and a corresponding aperture in the top wall of casing 388. Screw 381 has likewise a head 388 having a groove 389 therein for the engagement of a suitable tool in order that tension exerted by spring 385 may be varied as desired. The purpose of such variation will be more fully described hereinafter. 386 is also provided with a downwardly extend- Member ing portion 398 similar to extension 318 and provided correspondingly with a pointer 39|, extension 398 being passed through a slot 392.

Referring now to Figure 18 it will be seen that lever 38| is provided with a notch 394 (Figure 16) adapted to be engaged by a knife edge 395 comprising a portion of a link 396 which carries at its other end a corresponding knife edge 391 adapted to engage notch 333 of extension 332 of member 33|.

Thus from the foregoing, it will be readily understood that spring 385 through lever 38| and link 396 exerts a force on member 33| and consequently on lever 3 I1 as soon as the straight line relationship of pivots-331, 335 and knife edge 3I8 is disrupted, but that when such straight line relationship as disclosed in Figure 17 exists the component of force exerted by spring 385 is zero while the direction thereof is substantially parallel to the above mentioned straight line relationship. However, upon a decrease in pressure resulting in a downward movement of that end of lever 3|1 adjacent operating rod 385 and the consequent disruption of this straight line rela` tionship, an increasing force is exerted by spring 385 through link 396 to force member 33| outwardly and consequently move link 336 to move arm 348 in a downward direction. By suitable adjustment of screws 381 the force exerted by spring 385 may be adjusted exactly to compensate for the increasing tension of spring 362 and bellows 383 as the samelis increased by downward movement of block 351 by lever 3|1. Likewise, by suitable adjustment, the tension in spring 385 may be so increased as to provide an increasing force in excess of the decreased tension of spring 362 in order that when the abovefmentioned straight line relationship is disrupted, as such disalignment proceeds, the force component exerted by spring 385 is such as to overcome the force component of spring 362 suiciently to impart a snap action to the movement of arm 348 and its associated contacts. Likewise, as the pressure increases to move operating rod 385, the parts will move from the position shown in Figure 16 to that shown in Figure 17 with a snap action.

Referring now to the contact structure, secured to insulating block 35| is a pin 488 having a head 48|. Slidably mounted upon pin 488 is a bar of conductive material 482 provided with contacts 483. Bar 482 is provided with depending lugs 484 (Figure 22) positioned for engagement with suitable apertures 485 in insulating bar 35| to prevent rotation of bar 482 about pin 488, A spring 486 is positioned between head 48| of pin 488 and bar 482 and serves to bias bar 482 to its associated contacts in the Vdirection of insulating block 35|. Suitable stationary contacts 481 are mounted, as by means of nuts 488 and 483, in the top wall of casing 388. Leads 4|8 may be suitably secured, as by nuts 488 to provide electrical connection with the contacts 481, which connection will be bridged between the two contacts 481 by the opposed contacts 483 and bar 482. Thus, upon a closure of contacts 483 and 481 in the manner previously described, insulating block 35| is moved to the position shown in Figure 21, spring 486 is compressed and contacts 483 are held in comparatively tight engagement with contacts 481 by the normal resiliency of spring 486. Correspondingly, when the pressure actuating the mechanism to contact closing position is relieved, there will be a substantial movement of the parts hereinbe- "tacts which will not occur until the tension on spring 406 has been entirely-relieved and insulating bar 35| abuts bar 402 to move the same and its associated contacts 403 out of the position shown in Figure 17. Thus, a relatively firm contact pressure is maintained at all times until such time as the parts of the mechanismy have moved into a position where the resultant movement of the contact structure is relatively fast. Likewise, in the event of sticking between contact 403 and its associated contact 401, a pivotal movement of bar 402 is permitted against the pressure of spring 406 in order to effect a rocking movement of the contact and disengage the sticking thereof.

As best shown in FigureK 270, a scale plate generally indicated at 4|5 is provided on one side of casing 300. Scale plate 4I5 is comprised of two separate portions 4I6 and 4|1, each bearing indicia 4|8 and 4|9, respectively, thereon. Separate portions 4|6 and 4|1 are provided with apertures 420 and 42|, respectively, positioned in alignment with apertures 392 and 31|, respectively. Extensions 310 and 390 extend through apertures 42| and 420, respectively, and lugs 312 and 39| serve as pointers with respect to indicia 4|9 and 4I8, respectively. Scale plates 4|6 and 4|1 are each provided with a pair of vertically extending slots 425 and 426, respectively, through each of which is passed a screw 421 which screws in turn, engage suitable threaded apertures in the side wall of casing 300. Thus, it will be seen that by loosening screws 421 in slots 425, scale plate 4| 6 may be moved upwardly or downwardly within the limits of range of slots 425 and tha-t by loosening screws 421 in slots 426, scale plate 4|1 may be moved upwardly or downwardly within the range of slom 426. An'important advantage is achieved by this construction in that if the instrument is previously calibrated in the factory to operate at certain given 1conditions and these conditions are known, should `there be any discrepancy between the known settings and the indicia, such discrepancy may be readily corrected by a simple movement of the scale plate rather than as was hitherto the case, Va complete recalibration of the instrument.

Casing 300 may, if desired, be provided with mounting lugs 430 whereby it may be secured to any desired surface.

It will be understood that in connection with all the rforegoing described instruments embodying this invention suitable housings or casings may be provided in order to enhance the appearance of the instruments as well as protect the working parts.

In the foregoing description it has been set forth how the spring rate of the main adjusting spring and the operating bellows has been compensated. It is emphasized that the purpose of this invention is to compensate for the spring rates of all springs which affect the operation of the movable contact arm by the bellows. Thus the spring rates of spring 35 in the first modification, spring 208 in the second modification, spring |09 in the third modification, and spring 3|D in the fourth modification are compensated in the same manner and by the same spring.

Thus from the foregoing, it will be seen that there are herein provided a plurality of structures embodying the instant invention and achieving the objects thereof in a reliable and effective manner including many advantages of great practical importance.

As many additional embodiments may be made of the above described invention and as many modifications may be made in the embodiments hereinbefore described and shown in the accompanying drawings, it is to be understood `,that all matter hereinbefore described or shown'isto be 4interpreted merely as illustrative and not in a limiting sense.

I claim as my invention:

1. In a device of the character described, in combination, a fixed contact, a movable contact adapted to engage and disengage said fixed contact, means to move said movable contact, a plurality of levers connecting said means to said movable contact, said levers serving to transmit a relatively small movement of said means into a relatively great movement of said movable contact, said levers being so arranged that the fulcrums of a plurality of levers lie in straight ,line relationship with respect'to the component of force exerted by said means as said movable contact is moved into engagement with said fixed contact whereby upon displacement of said straight line relationship an amplification of movement of said movable contact results and upon resumption of said straight line relationship a relatively great forcel component is exerted said movable contact, in combination, a fulcrumed member movable by said means, a lever movable by said member and a second lever connected to said movable contact and movable by said first lever, said member vand said first lever lying in straight line relationship as said movable contact is moved into engagement with said stationary contact whereby a relatively decreasing movement of said means is`necessary to move said movable contact away from said stationary contact a relatively increasing amount.

3. In a switching Ymechanism, in combination, a fixed contact, a movable contact adapted to engage and disengage said fixed-contact, a resilient member carrying said movable contact, means `to move said resilient member and hence said of two or more of said plurality of levers lie inv straight line relationship with respect to the component of force exerted by said means as said contacts are moved into engagement, whereby a relatively large force is available for opening and closing said contacts, and a relatively large movement of said movable contact will occur after said straight line relationship has been disrupted.

4. In a switching mechanism, in combination, a fixed contact, a movable contact adapted to engage and disengage said fixed contact, a resilient member carrying said movable contact, means to move resilient member and hence said movable contact, a plurality of levers connecting said means to saidV member and serving to transmit a relatively small movement of said means into a relatively great movement of said member, said leversbeing so arranged that the fulcrums of two or more of said plurality of levers lie in straight line relationship with respect to the component of force exerted by said means as said contacts are moved into engagement, whereby upon displacement of said straight line 'relationship an amplification o1' movement of said resilient means results and upon resumption of said straight line relationship a relatively great force component is exerted against said resilient means to hold said contacts in engagement, said force being sufficient to warp said resilient means in such manner and to such degree that the resilience thereof is sufficient to hold said contacts in close engagement.

5. In'a switching mechanism including a xed contact, a movable contact and means to move said movable contact, Yin combination, a member movable by said means, a resilient member carrying said movable contact, a lever movable by said member and a second lever connecting said rst lever and said resilient means, the fulcrums of said levers lying in straight line relationship with respect to each other as said lmovable contact is moved into engagement with said stationary contact whereby upon displacement of said straight line relationship the movement of said movable contact is amplified with respect to the movement of said means, said levers when in straight line, relationship biasing said resilient member in such manner and to such a degree that the resiliency thereof serves to hold said contacts in engagement with a relatively substantial force.

6. In a switching device, in combination, a condition responsive means movable in response to change in the value of a condition, a member movable by said means, a lever movable by said member, a contact carried by said lever, and a fixed contact adjacent said movable contact and adapted to be engaged thereby, resilient means biasing said member in a direction opposite to the force exerted by said condition responsive means, and means to vary the tension in said resilient means, whereby to change the condition value requiredto move said member and hence said movable contact, said last mentioned means comprising a pivoted lever engaging an end of said spring, a roller carried by the opposite end of said last mentioned lever, a cam member adjacent said roller, said cam member having a serrated cam surface whereby said roller is engaged in one of said serrations and the number of possible positions thereof limited to the number of serrations, and means to vary the serration of I said cam member adjacent said roller.

7. An adjustment means for use in a switching mechanism including a movable contact, condition responsive means movable in response to changes in the yalueof a condition, a member operable by said condition-responsive means to move said contact and resilient means opposing the force exerted vby said condition responsive means; -comprised of a lever one end of which abuts an end of said resilient means, a cam member, the other end of said lever abutting said cam surface, and means to vary the dwell of said cam member adjacent said other end of `said lever, the surface of said cam member being parts, another of said parts having `an aperture 5 therein adapted to receive said pivot pin, said aperture having twosubstantially straight sides disposedy in acute angled relationship to each other, and a third sideconnecting said angled sides, said third side being convexly arcuate in 10 conlguration'with respect to and abutting Asaid pivot pin, whereby said pivot pin is fulcrumed on said arcuate side and said angled sides limit the movement thereof.

9. In a device of the characterdescribed com- 15 prising a plurality of parts pivotally mounted with respect to each other, an artificial knife edge mounting comprised of a pivot member having a substantially i'lat surface carried by one of saiduparts, another of said parts having an aper'- 20 ture therein adapted to receive said pivot member, said aperture having a convexly arcuate surface abutting said at surface, whereby said surface is in tangential relation to a point on said arcuate surface in any position with respect 25 thereto and said point serves as a fulcrum for movement of pivot member.

l0. In a switching mechanism, in combination, a supporting member, a condition responsive means movable in response to changes in the a0 value of a condition, mechanism operable thereby, resilient means opposing the movement of said condition responsive means, additional resilient means, associated with said mechanism compensating the increased force of said first`85.

mentioned resilient means upon movement of said'condition responsive means against the resiliency thereof, an indicator iixedly associated with said rst mentioned resilient means, a second indicator fixedly associated with said second n resilient means, a scale plate adjacent each of said indicators, a slot in each of said. scale plates .extending in thedirection of movement of said indicators and clamping means associated with each of said slots, and said supporting member 4,5

whereby upon movement of said indicator to a position corresponding to the value of a known condition either of said scale plates may be moved until a portion thereof indicative of said value is adjacent said indicator to calibrate said 50 mechanism without the necessity of internal adjustment thereof.

11. In a switching mechanism, in combination, a condition responsive element movable in response to changes in the value of a-condition, a 55 member movable by said element, resilient means opposing the movement of said member, `a plurality of levers movable by said member, a resilient member movable by one of said levers, a contact carried by said resilient member, a second 00 contact `adjacent said first mentioned contact and a spring connected to one of said levers and biasing said rst contact away from `Vsaid second contact, said levers being so arranged that the fulcrums of two or more lie in straight line rela- 65 tionship when said rst contact is in one of its moved positions but not when it is in its other moved position, said spring being so positioned as to' exert a force component in the direction of said straight line relationship whereby when 70 said relationship exists the force of said spring is ineffective to move said rst contact but when said straight line relationship is disrupted by said movement of said member movement of said levers and hence said contact is compensated by said spring against the increasing tension of said resilient means.

12. In a switching mechanism of the charac-` ter described, in combination, a condition responsive element movable in response to changes in the value of a condition, a member movable by said element, a lever movable by said member, a second lever movable by said first lever, said first and second levers lying in straight line relationship when said member is in a given position, a contact movable by said second lever, a fixed contact adapted to be engaged and disengaged by said first contact, a spring acting in opposition to the force exerted by said element and said member, and a second spring exerting a component of force in a direction parallel to the straight line relationship of said lever and opposed to the force exerted by said first spring, wherebysaid second spring is ineffective to move said levers but as said member moves in opposition to the force exerted by said first spring and the force exerted thereby increases said straight line relationship of said levers is disrupted to move said movable contact, said secondrspring exerting a force component on said movable contact and said levers sufficient to compensate for the increased force occasioned by said first spring.

13.7In a switching mechanism of the character described, in combination, a condition responsive element movable in response to changes in the value of a condition, a member movable by said element, a lever movable by said member, a second lever movable by said rst lever, said firstand second levers lying in straight line relationship when said member is in a given position, a contact movable by said second lever, a fixed contact adapted to be engaged and disengaged by said flrs contact, a spring acting in opposition to the fo ce exerted by said element and said member, a second spring exerting a component of force in a direction parallel to the straight line relationship of said lever and opposed to the force exerted by said first spring, whereby said second spring is ineffective to move said levers but as said member moves in opposition to the force exerted by said first spring and the force exerted thereby increases said straight line relationship of said levers is disrupted to move said movable contact, said second spring exerting a force component on said movable contact and said levers sufficient to compensate for the increased force occasioned by said first spring, and means to vary the force exerted by said first mentioned spring. Y

14. In a switching mechanism of the character described, in combination, a condition responsive element movable in response to changes in the value of a condition, a member movable by said element, a lever movable b'y said member, a second lever movable by said first lever, said first and second levers lying in straight line relationship when said member is in ,a given position, a contact movable by said second lever, a fixed contact adapted to be engaged and disengaged by said first contact, a spring acting in opposition to the force exerted by said element and said member, a second spring exerting a component of force in a direction parallel to the straight line relationship of said lever and opposed to the force exerted by said first spring, whereby said second spring is ineffective to move said levers but as said member moves in opposition to the force exerted by said first spring and the force exerted thereby increases said straight line relationship of said levers is disrupted to move said movable contact, said second spring exerting a force component on said movable contact and said levers sufficient to compensate for the increased force occasioned by said first spring, and means to vary the; force exerted \by said second mention l". spring.

V 15. In a switchingimechanism of the character described, in combination, a condition responsive element m'ovable inresponse `to changes in the value of a condition, a member movable by said element, a lever movable by said member, a second lever movable by said first lever, said first and second levers lying in straight line relationship when said member is in a given position, a contact movable by said'second lever, a fixed contact adapted to be engaged and disengaged by said first contact, a spring acting in opposition to the force exerted by said element and said member, a second spring exerting a component of force. in a direction parallel to the straight line relationship of said lever and opposed to the iorce exerted by said first spring, whereby said second spring is ineffective to move said levers but as said member moves in opposition to the force exerted by said first spring and the force exerted thereby increases said straight line relationship of said levers is disrupted to move said movable contact, said second spring exerting a force component on said movable contact and said levers suflicient to compensate for the increased force occasioned by said first spring, means to vary the force extended by said first mentioned spring, and means to vary the force exerted by said second mentioned spring.

16. In a device of the character described, a first member pivoted at one point to a support and at another point to one point on a second member, a control member having two control positions. said second member being pivoted at a second point to said control member, and means to rotate one of said first two members, said control member being in one of its control positions when said three pivot points are in a straight line, and in its other control position when said points are disaligned.

17. In a device of the character described, a

first member pivoted at one point to a support and at another point to one point on a second member, a control member having two control positions, said second member being pivoted at a second point to said control member, and condition responsive means pivoted to said first member relatively close to where said first member is pivoted to said support, said control member being in one of its control positions when said three pivot points are in a straight line, and in its other control position when said points are disaligned.

'18. Ina switching mechanism, in combination, a first member pivoted at one point to a support and at another point to one point on a second member, a control member, a movable switch contact, means whereby said movable Contact is carried by said control member including a resilient connection, a stationarycontact, said second member being pivoted at a second point to said control member, and means to rotate one of said first two members, said control member holding said switch contacts in engagement through said resilient connection when said three pivot points are in a straight line, said resilient connection holding said contacts in engagement during a substantial movement of said one of said members by said means to cause disalignment of said pivot points.

l19. In a device vof the character described comprising in combination, a resilient actuating element, a movable switch operating member, means including a toggle connectingsaid resilient actuating element to said switch operating member, and spring means acting on said member resisting movement of said toggle to dead center position, said spring means over compensating the spring rate of the resilient actuating element.

20. In a device of the character described, comprising in combination, a movable contact arm, 'a resilient condition responsive device, a lever pivoted on a support and adapted to be rotated about said support by said condition responsive device, a link pivotally connected at different points to said lever and said contact arm, said contact arm being in closed circuit position when said pivot points are aligned and in open position when theyare disaligned, and means compensating the spring rate of said condition responsive device.

21. In a switching mechanism, in combination, a movable contact arm, a movable contact carried thereby, a stationary contact positioned for cooperation therewith, a bellows, a lever pivoted about a support, said lever being adapted to be rotated in one directionby said bellows, a spring for rotating said lever in the opposite direction, a link pivotally connected at different points to said lever and said contact arm, said contact arm being in a position to close said contacts when said three pivot points are in a straight line and to open said contacts when said pivot points lare disaligned, and means to compensate the spring rates of said bellows and said spring.

22. In a switching mechanism, in combination,

i a movable contact arm, a movable contactcar- 50,disaligned, and means to compensate the spring rates of said bellows and said spring, said means comprising a spring so `connected as to exert no force on said bellows when said pivot points are aligned but to exert an increasing force on said bellows as said lever is rotated to ,disalign said pivot points.

23. In a switching mechanism, in combination, a contactl arm rotatably mounted at one end and carrying a movable contact at its other end by means of a resilient connection, a stationary contact positioned for cooperation therewith, a bellows, a lever pivoted about a support, said lever being adapted to be rotated in one direction by said bellows, a spring for rotating said lever in the opposite direction, a link pivotally connected at dierent points to said lever and said contact arm',.said contact arm being in a position to close said contacts whensaid three pivot points are in a straight line and to open said contacts when said points are disaligned, said contacts remaining closed due to said resilient connection until said lever has been rotated a short distance to disalign said pivot points after which they open, and means to compensate the spring rates of said bellows and said spring.

24. In a switching mechanism, in combination, a contact arm rotatably mounted at one end' and carrying a movable contact at its other end by means of a resilient connection, a stationary contact positioned for cooperation therewith, a bellows, a lever pivoted about a support, said lever being adapted to be rotated in one direction by said bellows, a spring for rotating' said lever in the opposite direction, a link pivotally connected at diierent points to said lever and said contact arm, said contactv arm being in a position to close said contacts when said three pivot points are in a straight line and to ope'n said contacts when said points are disaligned, said contacts remaining closed due to said resilient connection until said lever has been rotated a short distance to disalign said 'pivot points after which they open, and means to compensate the spring rates of said bellows and said spring, said means comprising a spring engaging the contact arm and tending to move it in a contact opening direction.

25. In a switching mechanism, in combination, a contact arm rotatably n ounted at one end and carrying a movable contact at its other -end by means of a resilient connection, a stationary contact positioned for cooperation therewith, a bellows, a lever pivoted about a support, said lever being adapted to be rotated in one direction by said bellows, a spring for rotating said lever in the opposite direction, a link pivotally connected at different points to said lever and said contact arm, said contact arm being in a position to close said contacts Whensaid three pivot points are in a straight line and to open said contacts when said points are disaligned, said contacts remaining closed due to said resilient connection until said lever has been rotated a. short distance to disalign said pivot points after which they open, and means to compensate the spring rates of said bellows and said spring, said means comprising a spring engaging said lever and exerting a force thereon in a direct line with said pivot points when they are in a. straight line, and in a. direction to assist said other spring when the pivot points are disaligned.

26. In a switching mechanism comprising in combination, a bellows, an operating member adapted to be moved longitudinally by said bellows, a main spring resisting such movement, a contact arm rotatably mounted at one end and carrying a movable contact at the other endby means of a resilient connection, a stationary conlever being pivotally connected to the other end of said third link, a second lever pivoted to a support, a double knife edge one end of which engages said second lever and the other end of which engages the other side of said operating v member directly opposite the point at which said rst lever is fulcrumed'to it, and a. compensating spring tending to rotate said second lever toward said operating member, ,said two links being aligned with each other andsaid first lever being aligned with said double knife edge when said contacts are closed at which time the compensating spring exerts no force tending to move said yoperating member longitudinally, said compensating spring exerting an increasing force on said operating member through said double knife edge as said operating member moves to disaiign said first lever and double knife edge and the two links thereby opening said contacts.

27. In a device of the character described comprising in combination, a pivoted lever, a resilient member for rotating said lever, a movable member, a toggle mounted between and carried by said movable member and lever, said movable member exerting a force through said toggle sumcient to compensate the spring rate of said resilient member, control means actuated by said 15 movable member, said control means being in one operative position when said toggle is in substantial alinement with the pivot for said lever, and means preventing said toggle and lever from going beyond said alined position in one direction.

28. In a device of the character described oomprising in combination, a condition responsive device, a main adjusting spring for. said condition responsive device, a movable cam, and a member engaging one end of said spring and forced thereby into engagement with the face of said cam, said cam face having a series of depressions into which said member seats whereby said cam cannot be accidentally displaced.

DANIEL G. TAYLOR. 

